The organic light-emitting diode (OLED) which is one of flat panel displays, is auto-luminescent, so that it has an excellent sight angle and contrast, compared with LCD, and it does not require a back light and can be prepared with simplified processes. As a result, a light thin display device can be produced with less electric energy power, and thus researches have been focused on it. The properties of OLED panel depend on the characteristics of an organic electroluminescent compound. Therefore, studies have been actively going on luminescent materials.
Luminescent materials are divided largely into two groups according to their functions; host materials and dopant materials. To produce a display device with the structure appropriate for upgraded EL property, a host material is doped with a dopant material to generate a luminescent layer. It is an urgent request to develop an organic EL display device with high efficiency and long lifetime, in particular it is strongly requested to develop an excellent host material with improved properties compared with the conventional light-emitting materials, considering EL needed for medium/large sized OLED panels. So, one of the most important tasks is definitely to develop an excellent host material.
It is preferable for a host material which acts as an energy and/or a solid solvent carrier to have high purity and a required molecular weight for vacuum deposition. In addition, it is also required for a host material to have high glass transition temperature and pyrolysis temperature to secure thermo-stability, and at the same time to have high electro-chemical stability for long lifetime. In order to generate an amorphous thin layer, a host material has to have a good adhesive power with other layers and materials nearby but has to avoid migration through layers.
Many of host materials have been reported so far and the most representative host materials are exemplified by diphenylvinyl-biphenyl (DPVBi) by Idemitsu-Kosan Co. Ltd. and dinaphthyl-anthracene (DNA) by Kodak Co. However, these materials still need to be improved in their efficiency, lifetime, and color purity, etc.

As an attempt to develop a host material with high efficiency and long lifetime, di-pyrenylfluorene (DPF) and bis-phenylanthracene-spirofluorene (BPA-SP) having the following structure have been introduced, but they cannot meet our expectation for luminous efficiency, lifetime and color purity.

For example, in the case of DPF presented by Cannon Inc. (Saitoh, A. et. al. Digest of tech. papers-SID 2004, 35, 686; US Patent No. US 2005236977), it exhibits excellent EL property (0.15, 0.14) and external quantum efficiency of 3.9% under the optimum doping condition, which is still not satisfactory for commercialization though. In the meantime, BPA-SP (Shen, W.-J. et. al. Chemistry of Materials, 2004, 16, 930; US Patent No. US 2002122900) exhibits the luminous efficiency of 2.67 cd/A and comparatively excellent color coordinate (0.15, 0.11), which is still not satisfactory for commercialization, either.
